Human MicroRNA as a potential therapeutic target in Alzheimer's disease Alzheimer's disease (AD) is the most common cause of dementia in the elderly. Current treatments provide only modest symptomatic relief and do not slow disease progression. Thus, new therapeutic strategies are needed. We propose to identify and validate members of a new class of drug targets. Major hallmarks of AD include amyloid plaques, neurofibrillary tangles, synaptic dysfunction and cognitive decline. These aberrations are believed to result, in part, from the overproduction of amyloid-beta peptide (A), a proteolytic product of the A precursor protein (APP). Dysregulation of proteins involved in A production may contribute to excess A deposition. Here, we propose the novel approach of targeting microRNA (miRNA) for therapeutic intervention. These are short, non-coding RNAs that act to inhibit protein expression by interacting with specific recognition elements in the 3'-UTR of targe transcripts. We hypothesize that specific miRNA species regulate endogenous levels of APP gene products and that disruption of miRNA-mediated regulation will modulate A levels. Specific Aim (SA) 1a will test the endogenous role of specific miRNAs in governing expression of APP. Rationale: We have recently discovered that specific miRNA (miR-101 and miR-153) regulate APP expression when delivered exogenously. To demonstrate the physiological relevance of this pathway, we will show that such interactions occur endogenously by using miRNA inhibitors and 'Target protector' experiments. Impact: Existence of such a regulatory pathway will stimulate research on its disease relevance. It will also open up therapeutic opportunities to limit APP/ A levels and prevent neurodegeneration in AD and Down syndrome. SA1b will assess how disruption of miRNA regulatory interactions with APP affects A homeostasis. Rationale: Since our focus is on APP and its role in A, we will examine how manipulation of endogenous miRNA-3'-UTR regulatory interactions affects downstream molecular pathways implicated in AD. We will assay the products of APP processing: APP and A levels. Impact: Modulation of these pathways would indicate that these miRNAs likely have endogenous regulatory roles that would make them attractive therapeutic targets. SA 2 will examine the effects of in vivo overexpression of miR-101 and miR-153 in an AD animal model. Rationale: Experiments outlined above will thoroughly assess the therapeutic potential of these miRNAs. The experiments outlined in this aim will directly test the preclinical suitability of thes miRNA for therapeutic modulation in relevant AD in vivo models. A suitable miRNA target would be expected to modulate A levels in a salutary fashion. Impact: Testing this will lend further validity to their status as therapeutic targets. Significance: The proposed experiments should provide strong evidence as to whether miRNA regulate APP expression at the exogenous and endogenous level, as well as in vitro and in vivo. These experiments will address whether manipulating the interactions of miRNA with the APP transcript produce salutary effects on downstream molecular pathways implicated in AD, and a potential use of these new drug targets for better therapeutic agents.